Wine country: California

In an effort to shed some light on how I study for WSET Diploma Course’s D3 exam, Le Club des Vins is running a series of posts covering wine regions. Today’s topic: California.


California is the number #1 wine state of the United States and located next to the Pacific Ocean. The potential of the vineyards is determined by what lies between it and the Ocean.

california wine country

In a nutshell

  • 80% of all US wine
  • 4th producer worldwide
  • 250.000 hectares
  • 140 AVAs
  • 63% black grapes
  • Home to largest wine company in the world: Gallo (6.3 million hl of wine each year)


Grapes were brought by Spanish missionaires. Most grapes were used to make altar wine and sweet fortified wine. By the late 19th century, many of the regions were producing wines. That came to an end in 1920, when Prohibition started, which stopped the production and possession of alcohol beverages till it was repealed in 1933. From 1930 till 1960, the wine industry rebuilt itself. Robert Mondavi was a key figure in the Californian wine history and did a lot to improve quality. In 1976, there was the Judgment of Paris, which really opened up the world’s eyes towards Californian wines.


Generally speaking, California has a Mediterranean climate. It is, however, greatly influenced by topography rather than latitude (32 – 42 degrees). The key factors on climate in California are the cold Pacific Ocean and the mountain ranges.

The water of the Pacific is so cold that it causes fog all summer and cools the land. The vineyards close to the water, like Carneros (south of Napa Valley) can be rather cool, whilst areas without influence of the coast (Calistoga and Central Valley) are much hotter. Rainfall is fairly low in growing season, drought is becoming a serious problem (hence, the fires).


Low rainfall combined with breezes from the coast reduce the risk of fungal diseases. However, there’s the bacterial disease spread by insects, Pierce’s disease. Weather hazards like spring frosts and wildfires are a serious threat too.

Pierce’s disease
Pierce’s disease is a bacterial disease caused by Xylella fastidiosa. The sharpshooter, an exotic plant pest is a key vector. The main symptom of Pierce’s disease in grapevines is leaf scorch; leaves become yellow.

Pierce’s disease can kill grapevines by blocking the plant’s water conducting system. The plant usually dies within two years. There’s no cure, prevention (by taking away infected vines) is the best option.

Source: more info

Wine law

California has about 140 AVAs.

  • 75% of the grape named on the label must be used
  • 100% of the grapes must come from California when ‘California’ is mentioned on the label
  • 85% of the grapes must come from the AVA mentioned on the label
  • 95% of the grapes must come from the vineyard mentioned on the label


In USA, it’s about AVAs: agricultural viticulture areas. California can be grouped into:

North Coast is the largest AVA of California and encompasses a part of Napa Valley, Sonoma Country, Mendocino County and Lake County.

Central Coast runs along the coast from San Francisco to Santa Barbara and includes Monterey, San Luis Obispo Country (Paso Robles)

Inland Valleys includes the large Central Valley where soils are fertile and yields are high. Lodi is probably one of the best known AVAs here, producing high quality old-vine Zinfandel.

Sierra Foothills is located east of San Francisco and covers 1 million hectare vineyards. Day time temperature can get as high as 40 degrees, but since we’re in the mountains here, the nights are cooler. High diurnal range. Known for old vine zinfandel. Additionally, varieties from the Rhone (GSM), Italy (sangiovese, aglianico) and Spain (tempranillo, verdelho) are also planted.

South Coast runs from Los Angeles to Mexico. Low latitude, so cooling influences are necessary: altitude, coastal breezes. Chardonnay, cab sauv, zinfandel and chenin.

Grapes & styles

Chardonnay and cabernet sauvignon are the two most planted grape varieties in California. Followed by pinot noir, zinfandel, merlot, colombard, syrah, pinot gris and sauvignon blanc.

Your turn now 

I always put a new region on instagram first. If you have any additions or comments on a region, please do share. You can drop a comment on instagram or on the website – see below. Your help is much appreciated!


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